We have seen reports in the past where a single victim was attacked by multiple source IP addresses in an ssh bruteforce attempt but usually it has been a single or at most a few source IP addresses.
Today we had 4 separate reports of an increase in ssh bruteforce attacks. Two of those reports stated that they were seeing lots of source hosts against a single victim. The isc.sans.org port 22 graph supports this as there has been a large increase in the source hosts seen in ssh scans during this month. If you can verify that this is a distributed, coordinated attack as some of us suspect that would be helpful. The type of coordination I would expect in this case is different systems using different account/password pairs.

“Almost every hour logcheck is emailing me about failed SSH logins. In the past the failed logins usually came from just one host at a time. fail2ban on my server would take care of this and I wouldn't worry. But now I'm seeing multiple servers all trying within minutes of each other and they'll only try a few times so fail2ban isn't working very effectively. It only appears to be for user "root" and "mysql".” (David)

“We're seeing unusually high inbound SSH scanning across our networks. The activity showed up on our radar 10/21 around 18:30 CDT (23:30 GMT). Some of the reverse lookups on scanning hosts suggest that these systems are compromised themselves (e.g. nagios.blah.tld or mail.blah.tld); many reverse lookups do not suggest this... At first blush, it appears that the majority of these remote scanners are in Europe or Eastern Europe.” (Bert)

“I see 2 or three ssh attempts in a day, and
suddenly I'm seeing one about every 3 minutes start almost an hour ago.
(reported around 6am MDT).
Anyone else seeing this stuff? Thanks.
“ (James)

UPDATE Coordination appears to be verified:

"What was more interesting than the distributed of the scans was that each host appeared to scan a different part of the dictionary. Normally we give them 11 tries and then iptables locks them out. When I looked at last week's log summary I was surprised to find several groups of 11 login name attempts which clearly began in different parts of the alphabet. This looks like an attempt to bypass the limited number of probes from any one host which most good firewall programs impose." (Ben)

From the ascii version of dshields port listing
We can see reported sources of ssh attacks have been climbing fairly steady with the highest number of sources reported occurring yesterday. Of course today’s data is not complete.